Set the Description. Set Trigger to A level starts. Leave Conditions empty. Press the New Action button and add the sound you wish to play.

This will play that sound at the start of any round, including breaks. If you want it to be only rounds, set the Conditions to isRound. If you want it to be only breaks, set the Conditions to !isRound.

There's no requirement for your sounds to be in any specific folder. They can be located anywhere in your computer's file system. First add the sounds by pressing the "New Sound" or "Import Sounds" button. After they are added, they can be referenced in an Event.

On the Database tab, press the "Backup" button. Make sure "Sounds folder" is checked. Then press OK, select a filename, and create the backup. That will include any audio files in your "sounds" folder in the backup. Audio files in other folders won't be included.